Power semiconductor devices fabricated from monocrystalline silicon carbide (SiC) have been widely investigated. As is well known in the art, monocrystalline SiC is particularly well suited for use in semiconductor devices, and in particular for power semiconductor devices, such as metal semiconductor field-effect transistors (MESFETs).
SiC has many characteristics which make it superior to silicon (Si) as a foundation material for a power semiconductor device. Specifically, SiC has a wider bandgap, a higher melting point, a lower dielectric constant, a higher breakdown field strength, a higher thermal conductivity and a higher saturation electron drift velocity than Si. These characteristics suggest that SiC-based power devices would operate at higher temperatures, higher power levels and with lower specific on-resistance than conventional Si-based power devices.
Although SiC is an excellent foundation material for power MESFET transistors, substrate material defects such as bulk crystal dislocations and dangling bonds at the material surface result in deep level and surface electron trapping effects that significantly limit the power performance and SiC MESFET reliability. Conventional SiC-based MESFETs exhibit high output conductance induced by poor carrier confinement in the channel region that enhances the probability of electron trapping in the buffer due to the aforementioned traps. This characteristic causes leakage current and degrades the gain and output power of SiC MESFETs.
Accordingly, a need exists for a SiC MESFET with improved electron confinement in the channel region to minimize the impact of deep level traps. In addition, the channel region surface requires an optimized passivation layer to eliminate dangling bond effects.